For many appliance and other equipment applications involving high volume unit production, such as furnace fans, blowers for air conditioners, washing machines, dryers, and the like, original equipment manufacturers continually strive for cost reduction in their products. One way is to reduce the cost of the motor utilized in the product. In such applications, single phase induction motors having at least one main winding and a start winding of the resistance start split phase type conventionally have been used due to the economy inherent in their manufacture. While the invention disclosed hereinafter works well with and is described as applied to single phase induction motors, its applicability is not restricted to those motors.
A single phase induction motor generally has oppositely disposed endshields. A stator assembly conventionally includes a single phase main winding and a start winding arranged in slots in a laminated iron stator core and those windings cause currents to be induced in a squirrel cage winding arrangement in slots of a motor rotor. The rotor conventionally is carried on a shaft journaled in suitably lubricated bearings carried by the endshields. Although the endshields can be attached to the stator assembly in a variety of ways, in the endshield design of this invention, the two endshields have four legs which insert into channels or grooves in truncated corners of the stator core. The leg ends are then secured in place with epoxy injected into the joints between the legs and the walls of the channels. Such constructions are described in U.S. Pat. Nos. 3,343,013 and 4,110,644.
It is known to provide aluminum endshields of a skeleton frame construction rather than a full enclosure, because the motor is located inside an appliance. Present skeleton endshields weigh approximately 1.5 pounds and use 15.7 cubic inches of aluminum in finished form. The structural characteristics of the skeleton design are considered adequate, as established by a long history of successful market application. However, prior attempts to reduce the amount of material in the endshield design has resulted in performance problems. In the past, the cost of aluminum has fluctuated dramatically, and there are and have been a number of attempts made either to reduce the amount of material in the endshields or to find substitute lower cost materials.
Whether substitute materials are employed or whether the amount of aluminum is reduced, a straight reduction in the quantity of material used or the substitution of material is not feasible because while the endshields become lighter, they also become structurally weaker. The lighter and weaker endshields often cannot withstand the stresses under which they are placed and therefore are unsatisfactory.
Clearly, it would be highly desirable to be able to substitute one material for another, for example, fiber reinforced plastic for A380 aluminum alloy or vice versa, in response to the development of a substantial differential in their respective costs. This has not been economically feasible with skeletal designs known heretofore. It is not necessary in such substitutions that the cross-sectional dimensions of the elements making up the skeleton be the same when the different materials are used. It is necessary for the inside and outside dimensions that are critical to the parts of the motor contained within the embrace of the endshields and are critical to the fitting of the motor to or in the appliance to be the same when different materials are used.
One of the objects of this invention is to provide skeletal endshields of a configuration that are adapted to be used in producing endshields made of different materials.
Another object is to provide such an endshield which is structurally sound so as to stand up to normal use.
Another object is to provide such an endshield which is economical to produce.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawings.